Food chemistry Flashcards
what are the two functional groups found in amino acids?
amino (-NH2) and carboxylate group (COOH)
How many amino acids are found in the body
20
Why are amino acids called alpha amino acids?
The amino, carboxylate and R groups are all attached to the same C atom. All human amino acids are alpha amino acids
What are essential amino acids
Must be provided directly through the proteins in the diet as human cells cannot synthesis them
What are non essential amino acids
Can be manufactured in the body from the dietary components.
Why are amino acids soluble in water
A a consequence of the polar amino and carboxylate functional groups
Why are amino acids amphiprotic
The amino group can act as a base and the carboxyl group can act as an acid
How are proteins formed
- Proteins are polymers formed by condensations reactions between amino acids.
- The amino group of one amino acid reacts with the carboxyl group of an adjacent amino acid
- A covalent bond is formed between them and a molecule of water is eliminated
What is the peptide linkage
The CONH group of atoms that links the constituent amino acid
What is the primary structure of proteins
The order of amino acids joined together in the polypeptide with peptide links between them (covalent bonds)
What is the secondary structure of proteins
- Parts of the chain can attract each other creating 3D shapes such as coiling and pleating.
- H bonds between polar NH group in one peptide like and the polar C=O in another peptide link can form at regular intervals
What is the tertiary structure of a protein?
-Some side groups are capable of forming bonds themselves with groups elsewhere on the protein chain
Types of bonds in tertiary structure?
- dispersion forces between non polar side chains
- H bonds between side chains (amino and c=O-NH2)
- Ion dipole between Nh3+ and cooh
- Ionic between NH3+ and COO-
- Di sulphide bridge (covalent) between non adjacent cysteine residues
What is the quaternary structure of a protein?
Multiple polypeptides chains held together with same bonding as tertiary structure
What is the general formula for a carb
Cx(H2O)y with H:0 ratio always 2:1
Why are monosaccharides soluble in water
They contain a number of polar hydroxy function groups (OH) enabling them to form hydrogen bonds with water.
What are the three most common monosaccharides
fructose, glucose and galactose with C6H12O6
How many chiral centres do glucose and lactose have
- This different causes molecules to behave differently in living organisms
Difference in glucose and galactose
Position of OH on 5th carbon has been flipped
Why is glucose the main source of energy
Glucose and its polymer starch is more rapidly digested that other forms of foods (ie lipids and proteins)
What is a disaccharide
Carbohydrate formed when two monosaccharides undergo a condensations reaction (with water eliminated)
Maltose, sucrose, lactose
Glucose plus glucose
Fructose and sucrose
galactose and lactose
Polysaccharides
Polymer carbohydrates made by linking monosaccharides into a chain
Why are polysaccharides insoluble in water?
Most of the hydroxy polar functional groups are used for other links in the polymer. This the large polymer has non polar characteristics.
Three most biological important polysaccharides
Glycogen starch and cellulose
Function of glycogen
Found in animals and acts as a glucose storage molecules. As energy is required glycogen is hydrolysed to yield glucose for respiration
Compare bp of glycogen
Polymer chains are less closely packed due to branching. Thus intermolecular forces are weaker (dispersion) therefore soft and lower mp
Function of starch
Glucose storage molecule in plants
Types of lipids
fats and oils
What are the constituents of fats and oils
C, H and small amounts of O occasionally
Difference between fats and oils
they have very similar chemical structures and are distinguished based on their physical states at room temperatures. Fats are solids. Oils are lipids
How are fats and oils formed
Condensation reaction between a single molecule of glycerol and three molecules of fatty acids. Called triglycerides
Compare reactivity of saturated and polyunsaturated fatty acids
saturated fatty acids are least reactive and accumulate in the body while unsaturated fatty acids are the most reactive and have the least accumulation in body cells
Physical properties compared of saturated and polyunsaturated fatty acids
FA chains are very closely packed, stronger dispersion forces, solid at room temp with a higher mp.
For unsaturated fatty acids the chains are far apart due to unsaturation, weaker dispersion forces, oil at room temperature and they have the lowest melting point.
What are essential fatty acids
Some polyunsaturated fats cannot be manufactured by the body and must be obtained from food.
What is the polarity and solubility of lipids
Most lipids are essentially non polar and insoluble in water. But they dissolve in non polar solvents
Difference between omega 3 and omega 6 fatty acids
- Unsaturated fatty acids with a double bond on the third last carbon atom in the hydrocarbon chain are classified as omega 3 fatty acids.
- In the double bond is on the sixth last carbon atom, they are classified as omega 6 fatty acids
What are the two classifications of vitamins
Water soluble and fat soluble vitamins
Implication of water soluble vitamins
Excreted by the body if they are not used, so they must be consumed as a regular part of the diet.
Implication of fat soluble vitamins
Can be stored in the body in fatty tissue for a long period of time
Dangerous to take excessive quantities as the body does not easily dispose of them
Are these vitamins considered essential
Yes as humans cannot synthesise them except for biotin (vitamin b&) and vitamin D (synthesised in skin after expose to UV radiation)
Difference between macronutrients and micronutrients
- The body requires macronutrients in relatively large quantities eg proteins triglycerides and carbohydrates
- micronutrients are essential for normal functions. Require relatively small amounts eg vitamins and minerals
Define metabolism
All the chemical reactions that occur within a living organism to maintain life.
Includes breakdown of substances to yield energy (hydrolysis and respiration) and synthesis of large molecules that are necessary for life (condensation)
Explain reaction rates and digestion
Chewing food increases its surface area speeding up digestion
Explain solubility and digestion
food consists of polar and non polar substances. Polar digested in aqueous acid solutions in the stomach but non polar digested in non polar environment of the intestines
Endo/exo for condensation and hydrolysis
Condensation reactions tend to be endothermic, requiring energy to form larger molecules
Hydrolytic reactions tend to be exoteric releasing energy as bonds are broken in the formation of smaller molecules
Define enzymes
Biological catalysts that accelerates the rate of chemical reaction in cells
Optical isomers and enzymes
- All enzymes in the body are chiral and many substrate molecules have more than one chiral centre, specific interactions with enzymes
- The enzyme can distinguish between the enantiomers of the chiral substrate as enantiomers have different 3D shapes
- Only one enantiomer might fit the active site so only one is biologically active
Induced fit
The active site changes slightly to accomodate to the substrate. The products leave the enzyme and the enzyme returns to its original shape
difference between cofactor and coenzyme
A cofactor is a metal ion or another nonprotein organic compound called a coenzyme
Role of coenzymes
Interact with the enzyme during hydrolysis and act as a carrier of electrons or specific groups of atoms. Change the surface shape of the enzyme and the binding properties of the active site to better interact with the substrate.
Enzyme in temp above optimum
Increased kinetic energy of the molecules, increased movement throughout the enzyme causes breakages of intermolecular forces. Disrupts tertiary and quaternary structures. Causes change in 3d shape of active site
ENyme in temp below optimum
Particles have less kinetic energy so less frequent collisions with insufficient energy to overcome the activation energy barrier
Compare GI of amylose and amylopectin
Amylose is a non branched polymer of glucose and not easily hydrolysed while amylopectin is a branched polymer of glucose and is soluble in h2o as can’t cil so easily hydrolysed, high GI
GI
Glycaemic index. Measure of the rate of hydrolysis of carb in food
Foods contain carbs compared with pure glucose which has 100 gi
Role of bile in hydrolysis of fats and oils
Bile contains an emulsifying agent with converts big fat globules into small droplets, increase SA therefore polar enzymes can hydrolyse fats easily, increasing rate of reaction
What causes rancidity
C=C double bonds are susceptible to chemical reactions such as oxidation sheer polyunsaturated lips can be oxidised to form short chain ketones and aldehydes and carbolic acids.
prevented by addition of antioxidants
Product of rancidity
Free radicals are small molecules with unpaired electrons that are formed by this press
Why is energy from combustion greater
incomplete absorption of food by body
Incomplete oxidation of some nutrients
Heat loss, some energy released by oxidation of glues is lost as waste heat
